Dirat at Tulūl basalt plain, Syria
Descending towards Syria's capital city of Damascus from the east,
around 30 miles out, the flight path passes over a plain of lava,
with a roughly circular 10 mile-wide patch of black basalt visible to
the south and a line of cinder cones leading from it in a roughly
north/south direction. This region located in the Rif Dimashq governate
of Syria is known as Dirat at Tulūl (ديرة التلول), meaning "Land of Hills".
The figures below show an aerial photograph of the area (left) in
natural colour and (right) overlaid by a geological map compiled by
a Soviet geological survey in 1964 . The red areas are recent
quaternary basalts, and are surrounded by earlier quaternary basalts
(lighter pink). The cinder cones lie in chains along fault lines that
probably provided conduits for magma. The red dot shows very
approximately the aircraft position in the above image.
The darkest area, representing the youngest lava flows, is known
as the Tulul al-Safa (the Al-Safa Hills). It covers 220 square km,
and contains at least 38 cinder cones, including many vents active
in the Holocene (within 12,000 years). Water is extremely scarce in
the Tulul al Safa, with only nomadic Bedou visiting occasionally.
The inhospitibility of the region has made it a refuge, historically
by the Druze in times of war. It was the last pocket of ISIL in the
area, captured by the Syrian Army on 17 November 2018 in the As-Suwayda
offensive.
Although called "tulul" (meaning "hills"), the elevation of the recent
lava area is only modest, as these images showing hillshade (with
x4 vertical emphasis, left) and overlaid with contours at 50ft intervals
(right) show.
The area is a little reminiscent of the lava plains of Oregon and
Idaho and particularly the Craters of the Moon National Park in
the Snake River Plain. Those lava plains are associated with
thinning of the crust and rifting due to tectonic activity (the
subduction of the Pacific plate under the North American plate). In
general, plate interactions can cause thinning of the crust, reducing
pressure on the mantle and resulting in melting, the buoyant melt
then rising within the crust. However, that alone does not account
for the volume of material in larger lava fields, which also invoke
a mantle plume (as in the case of the Eastern Snake River Plain,
which has been associated with the Yellowstone hotspot).
In the case of the Dirat at Tulūl lava field, which is a part of
the larger Ḥarrat al-Shām volcanic field, although the lava field is
close to the tectonic activity associated with the development of the
Red Sea and the Dead Sea Fault System, particularly north-south regional
extension parallel to the plate movements acting on existing
faults , . However, chemical and isotopic analysis of
the magma origins reveals that the Syrian basalts are difficult to explain
by lithospheric melting, and suggests rather an association with the
Afar mantle plume under Ethiopia/Yemen and the lateral transportation of
material northwards .
The Ḥarrat al-Shām (حَرَّة ٱلشَّام) volcanic field, also known as
the Black Desert, extends from Syria into Jordan and Saudi Arabia.
(There are several such "Harrats" on the Arabian Plate, of which the
Ḥarrat al-Shām is the largest.) The blue dotted line in the maps
here show the approximate boundary of the Harrat Ash Sham Volcanic
Province . The plate boundary between the African Plate
and the Arabian Plate is shown as the red dotted line. The Dead Sea
Fault System is a strike-slip fault along the plate boundary where
Arabia is moving northwards relative to Africa at around 6mm/year.